justlikeclockwork on "Image Centering"

Hi,

I am by no means comfortable with CSS, but can usually figure basic things out. For example, I figured out how to have the images I upload only show at about 65% their original size, but now I'm wondering how I can center them. Does anyone know a quick fix to this? I'm using the "Bueno" theme. An example of what I mean is here:

http://justlikeclockwork.org/portfolio/portraits/img_3386-edit-2/

Thanks in advance!